Commercial real estate has three primary lease structures: gross, NNN, and CAM. Each structure defines who pays for operating expenses and how those expenses are recovered. The accounting for each is different. The errors are different. The recovery process is different.
A property manager who manages a portfolio with all three structures needs three different processes. A property manager who applies the same process to all three will make errors.
This article explains the three structures, the accounting implications, and the management requirements for each.
The Three Structures
Gross Lease (Full-Service Lease)
In a gross lease, the tenant pays a single rent amount. The landlord pays all operating expenses: taxes, insurance, CAM, utilities, and maintenance. The tenant's cost is fixed. The landlord's cost is variable.
Accounting implication: The landlord absorbs all expense increases. The rent is set to cover expected expenses plus a margin. If expenses exceed the margin, the landlord's NOI is reduced.
Management requirement: Expense control is critical. The landlord must monitor expenses against the budget and identify variances early. There is no recovery mechanism for overruns.
Common in: Office buildings, medical office, some retail.
NNN Lease (Triple Net Lease)
In an NNN lease, the tenant pays base rent plus three nets: property taxes, insurance, and CAM. The tenant bears the cost of operating the property. The landlord's revenue is net of these expenses.
Accounting implication: The landlord must track expenses, allocate them to tenants, and reconcile estimates to actuals annually. The recovery process is the core accounting function.
Management requirement: Accurate expense tracking, correct allocation, timely reconciliation, and documented true-up statements.
Common in: Retail, industrial, single-tenant office.
CAM Lease (Modified Gross or Base Year Lease)
In a CAM lease (also called modified gross or base year), the tenant pays base rent plus a share of CAM expenses. Taxes and insurance may be included in the base rent or billed separately. The lease typically has a base year or expense stop.
Accounting implication: The landlord must track CAM expenses separately from taxes and insurance. The base year or expense stop determines the tenant's share of increases.
Management requirement: Separate tracking of CAM, taxes, and insurance. Correct base year calculation. Cap enforcement if applicable.
Common in: Office, mixed-use, some retail.
The Accounting Comparison
| Feature | Gross | NNN | CAM (Modified Gross) |
|---|---|---|---|
| Tenant pays | Fixed rent | Rent + taxes + insurance + CAM | Rent + CAM (taxes/insurance may be separate) |
| Landlord pays | All expenses | Nothing (net) | Base year expenses or expense stop |
| Recovery mechanism | None | Annual true-up | Annual true-up or monthly billing |
| Expense tracking | Budget vs. actual | Pool calculation and allocation | Pool calculation and allocation |
| Cap application | N/A | Tax/insurance caps possible | Controllable expense caps common |
| Complexity | Low | High | Medium |
Where Each Structure Fails
Gross Lease Failures
Expense overrun. The rent was set based on expected expenses. Actual expenses exceed the estimate. The landlord absorbs the difference. There is no recovery mechanism.
Budget variance. The landlord does not track expenses against the budget during the year. The variance is discovered at year-end. The NOI is lower than expected.
Deferred maintenance. The landlord defers maintenance to protect NOI. The property deteriorates. The tenant complains. The lease is not renewed.
NNN Lease Failures
Recovery errors. The expense pool is wrong. The allocation is wrong. The cap is not applied. The true-up is late. The tenant disputes. The property owes a refund.
Base year errors. The base year amount is wrong. The tenant pays too much or too little. The error compounds annually.
Gross-up errors. The building is not fully occupied. The variable expenses are not grossed up. The existing tenants subsidize the vacant space.
CAM Lease Failures
Cap enforcement. The controllable expense cap is not tracked. The tenant is billed for expenses above the cap. The tenant audits. The property owes a refund.
Pool misclassification. A capital expense is included in the CAM pool. The tenant is overbilled. The property faces a claim.
Base year confusion. The base year is not reset at renewal. The tenant pays the old base year amount instead of the new one. The property under-recovers.
Managing All Three in One Portfolio
A portfolio with all three structures requires three different management processes:
Gross leases require budget discipline and expense monitoring. The landlord's risk is expense overrun.
NNN leases require accurate expense tracking, correct allocation, and timely reconciliation. The landlord's risk is recovery error.
CAM leases require cap enforcement, pool validation, and base year management. The landlord's risk is cap violation and base year error.
The common requirement is a system that reads the lease, applies the rules, and tracks the expenses correctly for each structure.
The Komod.ai Approach
CAM leases. Controllable expenses are separated from uncontrollable. Caps are enforced. Base years are tracked and reset at renewal. The pool is validated against the lease exclusions.
The system reads the lease, determines the structure, and applies the correct rules. The property manager does not need to remember which lease is which structure.
Conclusion
CAM, NNN, and gross leases are three different structures with three different accounting processes. The errors are different. The management requirements are different. A portfolio with all three requires a system that handles all three correctly.
The fix is not three separate processes. It is one system that reads the lease and applies the correct rules automatically.
Komod.ai is an AI-native operating layer for the commercial real estate back office. The platform reads leases, invoices, and bank activity; performs deterministic calculations; and stages completed work for human approval. Nothing posts without you.